1. Field of the Invention
The present invention relates to a conductor pattern test apparatus for detecting a disconnection of a conductor pattern of an LCD (liquid crystal display) substrate or the like, or a short-circuit between conductor patterns.
2. Description of the Related Art
A regular LCD in which a TFT (thin film transistor) is used is presently very popular since a very high quality of image can be obtained by the LCD.
The LCD of this type has, for example, the following structure. That is, a number of TFTs are formed on a plate-like glass substrate by photolithography, and a number of LCD segments having pixel electrodes electrically connected to drain electrodes of these TFTs are situated on the glass substrate with gaps between the LCD segments and TFTs. An array of a great number of pixel units is formed by combining the TFTs with the LCD segments. More specifically, several hundred thousand pixel units each having a square shape with one side of several hundred micrometers, are arranged on a substrate, thus forming an LCD substrate.
Transparent conductive electrodes common to a great number of pixel units are arranged to face to each other on such an LCD substrate, with gaps therebetween, and then liquid crystal is sealed in the gaps, thus obtaining an LCD.
As the patterns of LCD substrates are fined down and the capacity thereof is increased, a fault such as disconnection or short-circuit of gate electrodes or drain electrodes of an TFT is naturally likely to occur, due to fine particles entering during the manufacture process. However, when such an error is detected after sealing the gap with liquid crystal by a test, no repair is no longer possible. Therefore, the test of disconnection or short-circuit in each electrode is carried out in the process stage of an LCD substrate.
In this test, the resistance of each gate electrode or drain electrode is measured, for example, before the LCD substrate is subjected to a later manufacturing step, so as to judge whether an error is based on a disconnection, or the resistance across adjacent gate electrodes or adjacent drain electrodes is measured to judge whether an error is based on a short-circuit.
However, with the conventional tester, only the conduction test for testing whether or not a gate electrode or a drain electrode is disconnected, and the insulation test for testing whether or not adjacent gate electrodes or adjacent drain electrodes are short-circuited are carried out. Under such circumstances, the fault position of the disconnection or short-circuit cannot be located with such a tester.
In order to repair a fault part, the fault position must be located before the repair, which is time and labor consuming. For example, as a fault position locating method, there is a technique in which the electrode detected to have a fault is magnified, and the fault position is searched by naked eye. However, with this fault position locating technique, it is difficult to automatize a series of manufacturing steps including the repair process which takes place after the location of the fault position, thus taking an extremely long time to complete all the steps including the repair.